1. Field of the Invention
This invention relates to nuclear fuel rod loaders which automatically load nuclear fuel pellets into fuel rods used in nuclear reactor cores.
2. Description of the Prior Art
The core of a nuclear reactor contains an assembly of fuel rods, arranged so as to generate controlled amounts of heat in specific regions of the reactor core. The fuel rods, approximately thirteen feet in length, each contain a column of nuclear fuel pellets extending substantially the full length thereof. Some of the columns of pellets are organized and arranged in segments, each segment containing different types of fuel pellets varying in quantity of uranium enrichment.
It is critical to the operation of the reactor that these segments of fuel pellets contain the correct type of uranium fuel, that the segments be of the correct longitudinal regions of the fuel rods. These factors are critical in view of the fact that the amount of heat generated in specific regions of the reactor core must be controlled to prevent any possibility of overheating. Additionally, location of certain types of fuel in certain longitudinal regions of the fuel rods is required in order to control the reaction and assist reactor shut-down. Thus, it is important that errors in loading or mixing of the different types of fuel pellets do not occur when the fuel pellets are loaded into the fuel rods.
Experience has shown that previous control methods do not provide the optimum of accuracy desirable in the nuclear industry for assemblage of nuclear fuel rods. Assembly processes and assembly equipment are desirable which fully insure the degree of quality control required for a reliable system of fuel rod assembly.
In many currently used loading systems, fuel pellets and fuel rods are assembled and organized on tables, stands and holders and the assembled rows of fuel pellets are manually propelled into the fuel rods. These systems have been modified with the use of various types of guide bushings developed to assist the operator in aligning assembled rows of fuel pellets with the center lines of the fuel rods so as to facilitate a smooth and damage-free transfer of the pellets into the fuel rods. However, these systems still involve the risk of human failure on the part of the operator and therefore may require multiple checks by other individuals to insure accurate assembly.
U.S. Pat. Nos. 3,940,908 and 3,965,648 disclose improvements over the above-discussed types of prior art systems and wherein preassembled rows of fuel pellets are transferred by mechanical fingers or vibrators into multiple fuel rods. With the apparatus disclosed in these patents, however, the rods themselves must still be placed by hand in the loading position. No provision has been made for automatically weighing the fuel pellets or measuring the lengths of the fuel pellets as they are loaded into the fuel rods. Additionally, no automatic safety controls are included in the loading sequence.
An improvement in systems for assembling nuclear fuel rods according to acceptable standards within the nuclear industry is realized with the improved automated nuclear fuel rod loading apparatus disclosed in U.S. Application Ser. No. 910,999--King et al., filed May 30, 1978, now U.S. Pat. No. 4,235,066, and assigned to the same assignee as the present invention. This apparatus incorporates a microprocessor control for automatically loading nuclear fuel pellets into fuel rods. Additionally, it automatically measures and records the weight and length of the row of pellets currently being loaded, indexes the fuel rods, transfers the proper rod into communicating relationship with the row of fuel pellets at the proper stage in the loading sequence, and moves to index another rod into position after loading of the previous rod has been completed. However, the fuel rod loading apparatus disclosed in the King et al. application provides for the assembly, weighing and transfer of only a single row of fuel pellets into one fuel rod at a time.
It is therefore an object of the present invention to provide new and improved apparatus effective for assembling a plurality of nuclear fuel pellets in columns, with each column containing specific types of nuclear fuel, and for sequentially loading the column into a plurality of fuel rods, and each column contains the correct types and amount of fuel.
Another object of the present invention is to provide new and improved apparatus effective for facilitating assembly of a plurality of nuclear fuel pellets including first and second elongated members, positioning the rows of fuel pellets in a communicating relationship with first and second fuel rods, transferring the pellets from the first elongated member into the first fuel rod through a guide bushing assembly and disengaging the guide bushing assembly from the loaded fuel rod and secondly transferring the pellets from the second elongated member into the second fuel rod through a guide bushing assembly and disengaging the guide bushing assembly from the second loaded fuel rod.
Another object of the present invention is to provide new and improved apparatus effective for automatically indexing a first plurality of fuel rods relative to a plurality of loading stations for receiving pellets, for transferring each rod into communicating relationship with associated means holding a row of fuel pellets at a predetermined stage in the loading sequence, and for indexing a second plurality of rods into loading positions after loading of the previous plurality of rods has been completed.
Another object of the present invention is to provide in the fuel rod loading apparatus, new and improved means for facilitating movement of pellets into fuel rods during assembly and avoiding damage or plugging of the pellets in the fuel rod during the loading sequence.
Another object of the present invention is to provide new and improved fuel rod loading apparatus effective for automatically imposing controls on the loading operation and interrupting the loading sequence in the event the assembled lengths of the rows of fuel pellets within the loaded fuel rods, or the cumulative weights of the pellets in each fuel rod do not fall within certain prescribed limits.